Certification ensures Quality
Since the specifications for PROFIBUS and PROFINET are open and standardized, it is possible for anyone to build and sell devices. However, not all devices are equal and to ensure that users get the quality of product they deserve, PI operates conformance programs. Enacted via the network of independent PI Test Labs and securely administered by PI itself, conformance testing ensures that devices meet relevant specifications and that interoperability is never an issue in the field. Certified devices are an end user's guarantee of quality.
Never buy an uncertified PROFIBUS device! In the case of PROFINET, certification is mandatory before a device can be offered for sale. Passive components can not be certified.